ext4: constify static data that is never modified

Constify static data in ext4 that is never (intentionally) modified so
that it is placed in .rodata and benefits from memory protection.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -2365,7 +2365,7 @@ static inline void ext4_update_dx_flag(struct inode *inode)
 	if (!ext4_has_feature_dir_index(inode->i_sb))
 		ext4_clear_inode_flag(inode, EXT4_INODE_INDEX);
 }
-static unsigned char ext4_filetype_table[] = {
+static const unsigned char ext4_filetype_table[] = {
 	DT_UNKNOWN, DT_REG, DT_DIR, DT_CHR, DT_BLK, DT_FIFO, DT_SOCK, DT_LNK
 };
 
@@ -3050,7 +3050,7 @@ extern int ext4_handle_dirty_dirent_node(handle_t *handle,
 					 struct inode *inode,
 					 struct buffer_head *bh);
 #define S_SHIFT 12
-static unsigned char ext4_type_by_mode[S_IFMT >> S_SHIFT] = {
+static const unsigned char ext4_type_by_mode[S_IFMT >> S_SHIFT] = {
 	[S_IFREG >> S_SHIFT]	= EXT4_FT_REG_FILE,
 	[S_IFDIR >> S_SHIFT]	= EXT4_FT_DIR,
 	[S_IFCHR >> S_SHIFT]	= EXT4_FT_CHRDEV,

fs/ext4/mballoc.c

@@ -357,7 +357,7 @@ static struct kmem_cache *ext4_free_data_cachep;
 #define NR_GRPINFO_CACHES 8
 static struct kmem_cache *ext4_groupinfo_caches[NR_GRPINFO_CACHES];
 
-static const char *ext4_groupinfo_slab_names[NR_GRPINFO_CACHES] = {
+static const char * const ext4_groupinfo_slab_names[NR_GRPINFO_CACHES] = {
 	"ext4_groupinfo_1k", "ext4_groupinfo_2k", "ext4_groupinfo_4k",
 	"ext4_groupinfo_8k", "ext4_groupinfo_16k", "ext4_groupinfo_32k",
 	"ext4_groupinfo_64k", "ext4_groupinfo_128k"

fs/ext4/super.c

@@ -1208,7 +1208,7 @@ static const struct fscrypt_operations ext4_cryptops = {
 #endif
 
 #ifdef CONFIG_QUOTA
-static char *quotatypes[] = INITQFNAMES;
+static const char * const quotatypes[] = INITQFNAMES;
 #define QTYPE2NAME(t) (quotatypes[t])
 
 static int ext4_write_dquot(struct dquot *dquot);
@@ -1422,7 +1422,8 @@ static ext4_fsblk_t get_sb_block(void **data)
 }
 
 #define DEFAULT_JOURNAL_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))
-static char deprecated_msg[] = "Mount option \"%s\" will be removed by %s\n"
+static const char deprecated_msg[] =
+	"Mount option \"%s\" will be removed by %s\n"
 	"Contact linux-ext4@vger.kernel.org if you think we should keep it.\n";
 
 #ifdef CONFIG_QUOTA

fs/ext4/sysfs.c

@@ -34,7 +34,7 @@ typedef enum {
 	ptr_ext4_super_block_offset,
 } attr_ptr_t;
 
-static const char *proc_dirname = "fs/ext4";
+static const char proc_dirname[] = "fs/ext4";
 static struct proc_dir_entry *ext4_proc_root;
 
 struct ext4_attr {
@@ -375,7 +375,7 @@ static const struct file_operations ext4_seq_##name##_fops = { \
 PROC_FILE_SHOW_DEFN(es_shrinker_info);
 PROC_FILE_SHOW_DEFN(options);
 
-static struct ext4_proc_files {
+static const struct ext4_proc_files {
 	const char *name;
 	const struct file_operations *fops;
 } proc_files[] = {
@@ -388,7 +388,7 @@ static struct ext4_proc_files {
 int ext4_register_sysfs(struct super_block *sb)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
-	struct ext4_proc_files *p;
+	const struct ext4_proc_files *p;
 	int err;
 
 	sbi->s_kobj.kset = &ext4_kset;
@@ -412,7 +412,7 @@ int ext4_register_sysfs(struct super_block *sb)
 void ext4_unregister_sysfs(struct super_block *sb)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
-	struct ext4_proc_files *p;
+	const struct ext4_proc_files *p;
 
 	if (sbi->s_proc) {
 		for (p = proc_files; p->name; p++)

fs/ext4/xattr.c

@@ -81,7 +81,7 @@ static void ext4_xattr_rehash(struct ext4_xattr_header *,
 static int ext4_xattr_list(struct dentry *dentry, char *buffer,
 			   size_t buffer_size);
 
-static const struct xattr_handler *ext4_xattr_handler_map[] = {
+static const struct xattr_handler * const ext4_xattr_handler_map[] = {
 	[EXT4_XATTR_INDEX_USER]		     = &ext4_xattr_user_handler,
 #ifdef CONFIG_EXT4_FS_POSIX_ACL
 	[EXT4_XATTR_INDEX_POSIX_ACL_ACCESS]  = &posix_acl_access_xattr_handler,